Slow query when using ORDER BY *and* LIMIT

I have a query that uses ORDER BY and LIMIT to get a set of image data
rows that match a given tag. When both ORDER BY and LIMIT are included
for some reason the planner chooses a very slow query plan. Dropping
one or the other results in a much faster query going from 4+ seconds ->
30 ms. Database schema, EXPLAIN ANALYZE and other information can be
found at http://pgsql.privatepaste.com/31113c27bf Is there a way to
convince the planner to use the faster plan when doing both ORDER BY and
LIMIT without using SET options or will I need to disable the slow plan
options to force the planner to use the fast plan?

I found some stuff in the mailing list archives that looks related but I
didn't see any fixes. Apparently the planner hopes the merge join will
find the LIMIT # of rows fairly quickly but instead it winds up scanning
almost the entire table.

Thanks,
Jonathan